Although female sterility has been induced in experimental animals by active immunization with sperm (Isojima, S., et al (1959) Science 129:44; Katsh, S. (1959) Am. J. Obstet. Gynecol. 78:276), and antibodies that react with human sperm have been found to be present in sera of infertile women (Franklin, R. R., and C. D. Dukes (1964) Am. J. Obstet. Gynecol. 89:6), no strong correlation has been found between the presence of such antibodies and naturally-occurring human female infertility (Tyler, A., et al (1967) Fertil. Steril. 18:153; Israelstam, D. M. (1969) Fertil. Steril. 20:275). However, Isojima et al (Isojima, S., et al (1968) Am. J. Obstet. Gynecol. 101:677) reported the finding that sera of infertile women inactivates human sperm motility in the presence of guinea pig complement. Approximately 17% of infertile women due to unknown causes had antibodies in their sera that inactivated human sperm motility in the presence of complement. No such antibody was detectable in sera of parous women. These findings led to a generally accepted hypothesis that the presence of such antibodies in sera of infertile women can be regarded as the cause of female infertility (Isojima, S., et al (1972) Am. J. Obstet. Gynecol. 112:199). Thus, the specificities and immunobioligical properties of antibodies present in sera of infertile women showing complement-dependent inactivation of sperm motility are of crucial importance for understanding the biological mechanism of female infertility. However, the activity of such antibodies in sera of infertile women is generally lower than a sperm immobilization titer of 1:200 ("200 SI.sub.50 ") (Isojima, S., and K. Koyama (1976) Excerpta Med. Intern. Congr. Ser. 370:11), and certain serum components of normal subjects showed non-specific binding with human sperm. Therefore, immobiological studies on infertility have been difficult to perform in further detail.